As additional information regarding cell-to-cell recognitions among oral bacteria is discovered, it is becoming increasingly clear that a dynamic but organized microbial community exists in the oral cavity. The part of this complex community studied in this laboratory pertains especially to microbial ecology. Both gram- positive an gram-negative bacteria are tested as coaggregation partners. The concept of highly specific partnerships advanced by this laboratory gained additional support with the evidence that strains of Bacteroides gingivalis, a presumed periodontal pathogen, coaggregates with Fusobacterium nucleatum and Eubacterium nodatum, strains, that are also associated with periodontal disease, but not with any other oral strains. Some coaggregations are inhibited by lactose, which adds to the growing number of sugar-inhibitable pairings among the oral bacteria. An intensive survey of strains of Veillonella from the tongue, buccal mucosa, and saliva revealed that veillonellae from the tongue coaggregate with Streptococcus salivarius, also a tongue inhabitant, but not with subgingival bacteria. Whereas, veillonellae from subgingival plaque coaggregate with other subgingival bacteria but not with S. salivarius. These results provide the first direct evidence that coaggregation is tightly coupled to the ability of a strain to colonize a specific econiche. The results of each of these investigative approaches are focused on understanding the relationship of cell surface recognitions among oral bacteria and their role in microbial ecology.